The present invention relates to a cylinder liner, and to a combination of a cylinder liner and a piston ring, suitable for use in internal combustion engines, such as diesel engines.
Cylinder liners in conventional internal combustion engines are made of steel, or cast iron, where, as for cast iron cylinder liners, both types are used that have, and do not have, a nitride layer formed on the surface thereof. Piston rings adapted to be combined with such cylinder liners, typically have had a hard Cr plating layer provided on a sliding surface thereof for sliding along the cylinder liners. With this combination, because a piston ring having a hard Cr plating film is excellent in abrasion resistance, and a cast iron cylinder liner provides enhanced sliding characteristics due to graphite and steadite, unique to cast iron, excellent scuffing resistance and sufficient abrasion resistance have been secured.
The applicants of the present patent patent application proposed in Japanese Patent Laid-Open Publications No. 7-180608 (1995) and No. 8-178068 (1996), respectively, implementation of internal combustion engines of a smaller size and a lighter weight, operating at a higher speed, than previously, and improvement of aggression resistance (capability of being resistant to aggression from the counterpart thereof sliding therealong) of the piston, by replacing the hard Cr plating film with a Crxe2x80x94N alloy PVD (physical vapor deposition) film.
Piston rings and cylinder liners in diesel engines have been looking to improved abrasion resistance because the operating conditions of the diesel engines are becoming severer due to such causes as exhaust emission regulations.
An object of the present invention is to provide a cylinder liner and more particularly the combination of a cylinder liner and a piston ring having excellent abrasion resistance, for use in an internal combustion engine, particularly in a diesel engine.
In order to achieve the object described above, the first means employed by the present invention is to provide a cylinder liner in an internal combustion engine where the piston ring slides along the inner circumferential surface of the cylinder liner, wherein the cylinder liner has an iron oxide film formed at least on a part of the inner circumferential surface of the cylinder liner. The second means employed by the present invention provides a piston ring having a metallic nitride film formed at least on a sliding surface thereof which slides along the cylinder liner.
The type of cylinder liner is either a dry type or a wet type, and the base material of the cylinder liner is either cast iron, or steel. The cast iron, as the base material of the cylinder liners, is typically flake graphite cast iron, but may be either one of nodular graphite cast iron, CV cast iron, eutectic graphite cast iron, white heart malleable cast iron, high-chromium cast iron, and black heart malleable cast iron. As for steel, any steel material may be usable, where recommendable steels may include machine structural carbon steels, such as S43C, S45C, sS48C and S50C of JIS (Japanese Industrial Standards), and high-carbon chromium bearing steels, such as SUJ2 of JIS. Heat treatment may be either one of partial chill-hardening and partial surface hardening of certain areas, such as dead points, on the inner circumferential surface of the cylinder liners, and overall quenching and surface quenching of the cylinder liners. The cylinder liners, either of steel, or cast iron, may be provided with the application of one or more treatments, e. g:, nitriding treatment, boride forming treatment, sulphurizing treatment, carburizing treatment, ionimplanting treatment, metal diffusion/vapor deposition treatment, melt-spray coating treatment, surface hardening build-up chemical conversion treatment (oxide coating treatment, phosphate coating treatment and molten-salt carbonizing treatment) and resin-impregnating treatment, by applying such treatment thereto before the forming of the iron oxide film, or compositely with the forming of the iron oxide film. In addition, a shot peening treatment can be applied before or after forming the iron oxide film.
The iron oxide film formed at least on a part of the inner circumferential surface of the cylinder liner, has a thickness of 0.5-100 xcexcm and comprises a compound layer mainly of Fe3O4 (also containing Fe2O3 and FeO) and a diffusion layer, or a single compound layer, or a single diffusion layer. The iron oxide film is formed by means of either one treatment from air plasma spray coating, molten nitrate treatment, and water vapor treatment. The iron oxide film has numerous pores of around 1-xcexcm diameter on its rough surface, thereby having a high oil-maintaining capability, resulting in excellent abrasion resistance due to a subsequent oiling effect, which in turn extends the life of the cylinder liners. The iron oxide film also is chemically stable, and thereby is resistant to corrosive abrasion.
The piston ring is formed, using either cast iron, or steel, as a base material. As the piston ring base material, specifically, a base material is used that is selected from materials either containing cast iron of FCD 500 or over, martensite stainless steel (e.g., containing Cr at 5 to 20 percent by mass, or mass %, C at 0.16 to 1.4 mass %, MO, V, Co, and Al), or Sixe2x80x94Cr steel.
The metallic nitride film of the piston ring is formed either on the cast iron base material or on a nitride layer formed on the base material. This nitride layer may protect the piston ring from being exposed after the film is worn off.
The metallic nitride may be preferably either one from Crxe2x80x94N alloy, Crxe2x80x94Bxe2x80x94N alloy, Tixe2x80x94N alloy, and Crxe2x80x94Bxe2x80x94Vxe2x80x94N alloy. Here, Crxe2x80x94N alloy and Crxe2x80x94Bxe2x80x94N alloy may include alloys that contain oxygen at 1 to 15 mass %, and carbon at 1 to 15 mass %, respectively, in a solid solution state within their crystal structures.
The metallic nitride film to be formed on the sliding surface of the piston ring that slides along the cylinder liner, may be formed by means of either PVD or CVD (chemical vapor deposition), such as sputtering and ion-plating methods. The film is a layer that improves scuffing resistance and abrasion resistance of the piston ring, and may have a thickness of 5-120 xcexcm.
When the piston ring is provided with a nitride layer, the nitride layer of a thickness of 5-120 xcexcm is preferably formed on an entire surface of the base material to prevent knocking abrasion that occurs on the upper and lower end surfaces of the piston by being knocked against a corresponding ring groove in the piston.
Alternatively, instead of forming metallic nitride film on a piston ring, a carbon-based film (diamond-like carbon, metal diamond carbon), plating (Cr plating, laminated Cr plating, composite plating), and melt-spray coating (plasma spray coating, Mo+Mo2C+NiCr, Mo+NiCrBSi, Mo+Mo2C+NiCrBSi, CrC/NiCr, and the like), can be formed respectively as a protective layer, or dry processed, whereby similar effects may be also obtained.
The cylinder liner, according to the present invention, is arranged to have iron oxide film formed by means of water vapor treatment at least on a part of the inner circumferential surface thereof, and the piston ring (first compression ring), according to the present invention, is arranged to have PVD film of either Crxe2x80x94N alloy, Crxe2x80x94Bxe2x80x94N alloy (containing oxygen at 1 to 15 mass %, and carbon at 1 to 15 mass %, respectively, in a solid solution state within their crystal structures), Tixe2x80x94N alloy, or Crxe2x80x94Bxe2x80x94Vxe2x80x94N alloy. The cylinder liner and the piston ring, according to the present invention exhibit effects in that they have excellent abrasion resistance and have enough endurance to be used for a long period of time, even in a diesel engine operating under severe running conditions.